The invention relates to a magnetic-tape-cassette apparatus having a magnetic head with a cylindrical curved head face, which is used for recording and/or playback of information having a significant relatively high frequency content. More particularly, the invention concerns such apparatus having a magnetic head unit which includes guides and height limiters especially arranged one to each side of the air gap to minimize azimuth error, so as to maximize high frequency response.
My co-pending application, referred to above and expressly incorporated herein by reference, discloses a magnetic head unit having guide surfaces which are cylindrically curved about axes generally parallel to the axis of the cylindrical head face, a tape height limiter arranged at an axial end of each guide for limiting movement of the tape laterally in the direction of the height limiter, and a control means for keeping a lateral edge of the tape in contact with the height limiters during tape transport. The two height limiters are so arranged relative to the magnetic head, that a line connecting the points where the guide surfaces adjoin the height limiters extends perpendicularly to a plane which extends through the air gap or gaps, which plane is situated at equal distances from the adjacent pole pieces of the magnetic head.
The apparatus disclosed in my co-pending application reduces aximuth errors, that is, errors which occur because the position of the air gap deviates from a perfectly perpendicular position relative to the lateral edge of the magnetic tape, to a level so low that they have little or no undesired effect. This is accomplished by maintaining the connecting line between the above described points of the height limiters exactly perpendicular to the relevant plane through the head air gap. This construction provides the advantage that no further adjustment of the head unit is necessary during manufacture of the apparatus. Another advantage is that the transverse position of the track on the magnetic tape, relative to the air gap, is maintained accurately during tape transport. This construction thus enables magnetic tape cassettes recorded on one magnetic tape cassette apparatus to be played back on another apparatus without reproduction errors. To maintain the edge of the tape with the height limiters, my co-pending application discloses a control means comprising two plate springs which are each situated at an axial end of an associated tape guide and are each biased against the axial end of the relevant tape guide by a spring. This arrangement requires that the spring constant and the location of the plate springs must be chosen carefully to ensure that the tape guiding assembly provides the desired effect.